Aircraft and landing gear provided with at least one pair of shock absorbers, and a method performed by said landing gear

Abstract

Landing gear for an aircraft, the landing gear having at least one pair of shock absorbers comprising a first shock absorber and a second shock absorber, each shock absorber comprising a cylinder defining an inside space and a rod carrying a piston, the inside space being subdivided at least into a “primary” chamber and into a “secondary” chamber, the shock absorber including at least one throttling orifice putting the secondary chamber into fluid flow communication with the primary chamber. The primary chamber of the first shock absorber is connected to the secondary chamber of the second shock absorber of the pair by a first pipe, and the secondary chamber of the first shock absorber of the pair is connected to the primary chamber of the second shock absorber of the pair by a second pipe.

Claims

1. Landing gear for an aircraft, the landing gear comprising: a longitudinal bearing first skid and a longitudinal bearing second skid; a front cross-member and a rear cross-member, each of the front and rear cross-members extending transversely and suitable for connecting the first skid and the second skid to a fuselage of the aircraft, each of the front and rear cross-members having a first branch connected to the first skid and a second branch connected to the second skid, the first skid and the second skid situated transversely on either side of a vertical anteroposterior plane of symmetry; and a pair of shock absorbers comprising a first shock absorber and a second shock absorber arranged transversely on either side of the anteroposterior plane, each shock absorber attached to one of the front and rear cross-members, each shock absorber comprising a cylinder defining an inside space and a rod carrying a piston, the inside space subdivided at least into a primary chamber possessing an inside volume that decreases when the rod is pushed into the cylinder and into a secondary chamber, each of the primary and secondary chambers filled with a fluid, each shock absorber including a throttling orifice fluidly connecting the secondary chamber and the primary chamber, each piston defining at least part of one of the primary and secondary chambers of the corresponding shock absorber in order to move the fluid, wherein the primary chamber of the first shock absorber is directly connected to the secondary chamber of the second shock absorber via a first pipe, and the secondary chamber of the first shock absorber is directly connected to the primary chamber of the second shock absorber via a second pipe, wherein each of the first and second pipes opens out into a primary or secondary chamber via a pipe section, each throttling orifice opening out into a primary or a secondary chamber via a throttling section, each pipe section having an area greater than an area of each throttling section.

2. The landing gear according to claim 1, wherein the rod is fastened to at least one of the cross-members and the fuselage, and the cylinder is fastened to the other of the cross-member and the fuselage.

3. The landing gear according to claim 1, wherein the cylinder fluid flows through the first and second pipes to damp vertical movement in a landing mode of the aircraft, and wherein the cylinder fluid flows through the throttling orifice of each of the shock absorbers to damp roll movement in a roll mode of the aircraft.

4. The landing gear according to claim 1, wherein the first shock absorber and the second shock absorber are both fastened to the front cross-member or are both fastened to the rear cross-member.

5. The landing gear according to claim 4, wherein the first shock absorber and the second shock absorber are fastened respectively to the first branch and to the second branch of the front cross-member or of the rear cross-member.

6. The landing gear according to claim 1, wherein the first shock absorber is fastened to one of the front and rear cross-members and the second shock absorber is fastened to the other of the front and rear cross-members.

7. The landing gear according to claim 6, wherein the first shock absorber is fastened to the first branch of one of the front and rear cross-members and the second shock absorber is fastened to the second branch of the other of the front and rear cross-members.

8. The landing gear according to claim 1, further comprising: a first check valve positioned in the first pipe for preventing fluid from passing from the second shock absorber to the first shock absorber and for allowing fluid to pass from the first shock absorber to the second shock absorber, and a second check valve positioned in the second pipe for preventing fluid from passing from the first shock absorber to the second shock absorber and for allowing fluid to pass from the second shock absorber to the first shock absorber.

9. The landing gear according to claim 1, wherein at least one of the front and rear cross-members is a continuous cross-member having a central portion extending between the first and second branches.

10. The landing gear according to claim 1, wherein at least one of the front and rear cross-members is a discontinuous cross-member having an empty space between the first and second branches of the cross-member.

11. The landing gear according to claim 1, wherein each piston of the first and second shock absorbers includes the throttling orifice to fluidly connect the first and second chambers.

12. The landing gear according to claim 1, wherein the piston is interposed between the primary chamber and the secondary chamber.

13. The landing gear according to claim 1, wherein the first shock absorber and the second shock absorber are identical.

14. An aircraft having a fuselage connected to landing gear, wherein the landing gear is according to claim 1.

Description

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

(1) The invention and its advantages appear in greater detail from the following description of embodiments given by way of illustration and with reference to accompanying figures, in which:

(2) FIG. 1 is a view of an aircraft provided with landing gear of the invention;

(3) FIG. 2 is a view of landing gear of the invention having a pair of shock absorbers arranged on a discontinuous cross-member;

(4) FIG. 3 is a view of landing gear of the invention having a pair of shock absorbers arranged on a continuous cross-member, each shock absorber having a piston carried by a rod connected to a cross-member;

(5) FIG. 4 is a view of landing gear of the invention provided with a pair of shock absorbers comprising two shock absorbers arranged respectively on two cross-members;

(6) FIG. 5 is a view of landing gear of the invention having a pair of shock absorbers arranged on a continuous cross-member, each shock absorber having a cylinder connected to a cross-member;

(7) FIGS. 6 to 9 are views explaining the operation of the invention;

(8) FIGS. 10 to 12 are views showing a pair of shock absorbers including check valves; and

(9) FIG. 13 is a view of landing gear of the invention having four attachment points and including a pair of shock absorbers arranged on a continuous cross-member.

(10) Elements present in more than one of the figures are given the same references in each of them.

DETAILED DESCRIPTION OF THE INVENTION

(11) It should be observed that three mutually orthogonal directions X, Y, and Z are shown in the figures.

(12) The first direction X is said to be longitudinal. The term “longitudinal” relates to any direction that is substantially parallel to the first direction X.

(13) The second direction Y is said to be transverse. The term “transverse” relates to any direction substantially parallel to the second direction Y.

(14) Finally, the third direction Z is said to be in elevation. The term “in elevation” relates to any direction substantially parallel to the third direction Z.

(15) FIG. 1 shows an aircraft 1 and more particularly a rotorcraft.

(16) The aircraft 1 has a fuselage 2 that extends longitudinally along a vertical anteroposterior plane P1 of symmetry. The fuselage 2 is also secured to skid landing gear 5. In particular, the landing gear 5 is connected to frames 3 of the fuselage 2, that can be seen in FIGS. 2 to 5.

(17) It should be observed that a portion of the fuselage 2 is shown as being transparent in FIG. 1 in order to enable the landing gear 5 to be seen.

(18) The landing gear 5 has a first longitudinal bearing skid 6 referred to as “first skid” and a second longitudinal bearing skid 7 referred to as “second skid” arranged on either side of the anteroposterior plane P, possibly in symmetrical manner.

(19) Under such circumstances, the landing gear has two cross-members 10, each extending transversely and connecting the first skid 6 and the second skid 7 to the fuselage. In particular, the landing gear 5 has a front cross-member 11 and a rear cross-member 12.

(20) Each cross-member 10 is provided with a first branch 16 that is secured to the first skid 6 and a second branch 17 that is secured to the second skid 7. The first branch 16 and the second branch 17 of a given cross-member are arranged on either side of the anteroposterior plane P1, possibly in symmetrical manner.

(21) The branches are sometimes referred to as “downward branches” insofar as these branches extend from the central portion towards a skid going towards the ground. The branches extend at least in elevation from a top to a foot secured to a skid. Each branch may comprise one or more tubes, and possibly one or more sleeves, together with means for connection to a skid.

(22) Furthermore, each cross-member shown diagrammatically in FIG. 1 is continuous. Such a continuous cross-member has a central portion 13 that is substantially rectilinear and that is secured to the first branch 16 and to the second branch 17.

(23) Nevertheless, and with reference to FIG. 2, at least one cross-member may be a discontinuous cross-member. Under such circumstances, an empty space 14 lies between the first and second branches 16 and 17 in the vicinity of the anteroposterior plane P1.

(24) Independently of the nature of the cross-members and with reference to FIG. 1, the landing gear 5 is connected to a carrier structure of the aircraft by means of its cross-members.

(25) By way of example, each cross-member is thus fastened to a frame of the aircraft by at least one attachment system 100.

(26) For landing gear having three attachment points of the type shown in FIG. 1, one cross-member is fastened via two attachment systems 101 and 102 to a frame, while the other cross-member is fastened via at least one attachment system 100 to another frame.

(27) Nevertheless, the landing gear may have four attachment points. FIGS. 4 and 13 show examples of such landing gear.

(28) In the invention, and with reference to FIG. 3, the landing gear 5 is provided with a shock absorber arrangement 20.

(29) The shock absorber arrangement 20 comprises at least one pair 25 of shock absorbers. FIG. 3 shows a single pair of shock absorbers. Nevertheless, the landing gear may have a plurality of pairs, and for example it may have a respective pair of shock absorbers arranged on each of the cross-members.

(30) With landing gear having three attachment points, at least one shock absorber pair may be arranged on a cross-member having a single attachment point.

(31) Each pair 25 of shock absorbers has a first shock absorber 31 and a second shock absorber 32. The first and second shock absorbers 31 and 32 are arranged on either side of the anteroposterior plane P1, possibly in symmetrical manner. The first and second shock absorbers 31 and 32 may possibly be identical.

(32) The first shock absorber 31 and the second shock absorber 32 of a pair are each interposed between a cross-member and the fuselage of the aircraft.

(33) Thus, the first shock absorber 31 and the second shock absorber 32 are each fastened to a cross-member, specifically a cross-member that may be continuous or discontinuous depending on the variant.

(34) In the first alternative shown in FIG. 3, the first shock absorber 31 of a pair 25 is fastened to the first branch 16 of a cross-member. The second shock absorber 32 of the pair 25 is then fastened to the second branch 17 of the same cross-member.

(35) Nevertheless, in the second alternative shown in FIG. 4, the first shock absorber 31 of a pair 25 is fastened to one cross-member, while the second shock absorber 32 of the pair is fastened to the other cross-member.

(36) By way of example, the first shock absorber 31 is fastened to the first branch 16 of one cross-member, specifically the front cross-member in FIG. 4. The second shock absorber 32 is then fastened to the second branch 17 of the other cross-member, specifically the rear cross-member.

(37) Furthermore, and with reference to FIG. 3, each shock absorber 31, 32 of a pair includes a cylinder 40 that defines an inside space 41. The shock absorber 31, 32 also has a rod 50 carrying a piston 55 that is received in the inside space 41. The piston 55 and the cylinder 40 can move relative to each other in translation. Thus, the piston 55 slides in the inside space 41, or the cylinder 40 slides along the piston 55.

(38) The rod 50 may be a through rod, i.e. a rod that passes right through the piston so as to reach a guide of the cylinder. This characteristic makes it possible to obtain chambers of identical sections, each section being taken on a plane perpendicular to the axis of the rod and parallel to a face of the piston.

(39) In a first embodiment shown in particular in FIG. 3, at least one shock absorber 31, 32 has a first attachment system 80 fastening the rod 50 of the shock absorber 31, 32 to a cross-member 10. Under such circumstances, a second attachment system 81 fastens the cylinder 40 of the shock absorber 31, 32 to said fuselage 2.

(40) For example the first and/or second attachment system may comprise at least one hinge, or indeed a ball joint hinge.

(41) In a second embodiment shown in particular in FIG. 5, at least one shock absorber 31, 32 has first attachment means 90 fastening the cylinder 40 of the shock absorber 31, 32 to a cross-member 10. In addition, second attachment means 91 fasten the rod 50 of the shock absorber 31, 32 to the fuselage 2.

(42) By way of example, the first and/or second fastener means may comprise at least one hinge, or indeed a ball joint hinge.

(43) Furthermore, and with reference to FIG. 6, the inside space 41 of each shock absorber is subdivided at least into a chamber 42 referred to as a “primary” chamber and into a chamber 44 referred to as a “secondary” chamber. The primary chamber and the secondary chamber are filled with a fluid, such as oil or a gas, for example.

(44) The primary chamber 42 of a shock absorber possesses an inside volume 43 that decreases when the rod 50 is pushed into the cylinder 40, i.e. when the shock absorber retracts. Such retraction amounts to shortening the length of the shock absorber lying in elevation between the two ends of the shock absorber. Conversely, the inside volume 43 of the primary chamber increases when the rod 50 tends to leave the cylinder 40, i.e. when the shock absorber extends.

(45) Furthermore, each shock absorber has at least one throttling orifice 60 that puts the secondary chamber 44 into fluid flow communication with the primary chamber 42.

(46) Under such circumstances, the piston 55 of a shock absorber defines in part at least one chamber for moving the fluid within the shock absorber, possibly from one chamber to the other chamber through at least one throttling orifice 60.

(47) For example, the piston 55 has at least one throttling orifice 60 putting the primary chamber 42 into fluid flow communication with the secondary chamber 44 of the shock absorber. The throttling orifice passes right through the piston.

(48) In addition, the piston 55 is interposed between the primary chamber 42 and the secondary chamber 44. The piston 55 then defines the secondary chamber and the primary chamber in part.

(49) Under such circumstances, one chamber of a shock absorber is a top chamber situated above the other chamber, which represents a bottom chamber. In the embodiment of FIG. 6, the primary chamber of a shock absorber is a top chamber, the secondary chamber of the shock absorber being a bottom chamber. In the embodiment of FIG. 5, the primary chamber of a shock absorber is a bottom chamber, the secondary chamber of the shock absorber being a top chamber.

(50) Furthermore, and independently of the embodiment, the primary chamber 42 of the first shock absorber 31 in a pair is in fluid flow connection with the secondary chamber 44 of the second shock absorber 32 of that pair via a pipe 70 referred to as a “first” pipe 71. Likewise, the secondary chamber 44 of the first shock absorber 31 is in fluid flow connection with the primary chamber 42 of the second shock absorber 32 via a pipe 70 referred to as a “second” pipe 72.

(51) Each chamber of the first shock absorber is then in fluid flow communication with a chamber of the second shock absorber via a respective pipe.

(52) In addition, each pipe 70 opens out into a chamber via a flow section referred to as a “pipe” section 73. Each throttling orifice 60 opens out into a chamber via a flow section referred to as a “throttling” section 61. Under such circumstances, each pipe section 73 may present an area referred to as the “pipe” area that is greater than an area referred to as the “section” area of each throttling section 61.

(53) FIGS. 7 to 10 illustrate the operation of landing gear of the invention. This illustration is based on the embodiment of FIG. 6. Nevertheless, the various embodiments shown in FIGS. 2 to 5 operate in similar manner.

(54) With reference to FIG. 7, during a landing mode of operation, the pistons of the first and second shock absorbers 31 and 32 of a pair move relative to the associated cylinders, which movements are represented by arrows 200. These movements are of the same kind.

(55) In FIG. 7, when the fuselage moves down towards the landing gear, the pistons tend to reduce the volume of the primary chamber in each shock absorber while the shock absorber is retracting. Under such circumstances, the fluid contained in a primary chamber of a shock absorber tends to be discharged to the secondary chamber of the other shock absorber as represented by arrows 201. The flow of fluid within the throttling orifices is little or nothing.

(56) Conversely, and with reference to FIG. 8, during a roll mode of operation, the pistons of the first and second shock absorbers 31 and 32 in a pair perform respective movements of different kinds relative to the associated cylinders that are represented by arrows 202 and 203.

(57) In FIG. 8, a roll movement ROT causes the first shock absorber 31 to retract and the second shock absorber 32 to extend. The piston of the first shock absorber 31 tends to expel the fluid contained in the primary chamber of the first shock absorber into the first pipe. In contrast, the piston of the second shock absorber 32 tends to expel the fluid contained in the secondary chamber of the second shock absorber into the first pipe. As a result, these opposing actions tend to prevent fluid flowing within the pipes 70. Under such circumstances, the fluid flows within the shock absorbers 31, 32 through the throttling orifices.

(58) FIG. 9 is a graph plotting the travel speed V of the piston of a shock absorber relative to the associated cylinder along the abscissa axis in meters per second, and plotting the opposing force F generated by the shock absorber up the ordinate axis in newtons.

(59) The pipes 70 that have been installed serve to dissociate the roll mode of operation from the landing mode of operation in each shock absorber. A zone Z1 shows that the invention makes it possible to obtain a shock absorber that delivers a large opposing force for a slow travel speed during the roll mode of operation. The pistons of a pair of shock absorbers move in opposition and thus oblige the fluid to pass through the throttling orifices.

(60) Conversely, a zone Z2 shows that the invention makes it possible to obtain a shock absorber that provides little opposing force for a fast travel speed in the landing mode of operation. Specifically, the pistons of a pair of shock absorbers move in identical directions allowing the fluid to flow in the pipes.

(61) Furthermore, and with reference to FIG. 10, the landing gear 5 includes a device tending to limit rebounding of the aircraft while landing.

(62) Specifically, the first pipe 71 includes a first check valve 96 for preventing fluid from passing from the second shock absorber 32 to the first shock absorber 31 while allowing fluid to pass from the first shock absorber 31 to the second shock absorber 32. For example, the first check valve 96 opens out into the primary chamber 42 of the first shock absorber 31.

(63) Likewise, the second pipe 72 has a second check valve 97 for preventing fluid from passing from the first shock absorber 31 to the second shock absorber 32 and for allowing fluid to pass from the second shock absorber 32 to the first shock absorber 31. For example, the second check valve 97 opens out to the primary chamber 42 of the second shock absorber 32.

(64) Each check valve may comprise a ball 98 and a perforated seat 99, the ball 98 being suitable for closing a perforation in said seat in a closed position and not closing said perforation in an open position.

(65) With reference to FIG. 11, when the fuselage comes closer to the landing gear during the landing mode of operation, the check valves open and thus allow the fluid present in the primary chamber of each shock absorber in a pair to go into the secondary chamber of the other shock absorber in the same pair of shock absorbers.

(66) In contrast, and with reference to FIG. 12, when the fuselage tends to rebound, the check valves close. The fluid then passes through the throttling orifices, thereby effectively braking the rebound of the aircraft.

(67) Naturally, the present invention may be subjected to numerous variations as to its implementation. Although several embodiments are described, it will readily be understood that it is not conceivable to identify exhaustively all possible embodiments. It is naturally possible to envisage replacing any of the means described by equivalent means without going beyond the ambit of the present invention.

(68) For example, landing gear may include at least two pairs of shock absorbers. In an embodiment, one shock absorber in each pair may be connected to a first branch of a cross-member while the other shock absorber is connected to a second branch.

(69) A single cross-member may also have a plurality of pairs of shock absorbers. Likewise, each cross-member may have at least one pair of shock absorbers.

(70) In addition, FIGS. 1, 2, 3, and 13 show a pair of shock absorbers arranged on a front cross-member. Nevertheless, the shock absorbers of a pair may be arranged on a rear cross-member.